PEX tubing is prohibited from being installed within the first how many inches of piping connected to a water heater?

The correct answer indicates that PEX (cross-linked polyethylene) tubing is prohibited from being installed within the first 18 inches of piping connected to a water heater. This requirement is in place primarily due to the potential for high temperatures in that immediate vicinity, which could exceed the maximum temperature rating for PEX. Water heaters operate at higher temperatures, especially during the initial heating cycle, and the heat can negatively affect the structural integrity of the PEX tubing, potentially leading to failure or leaks.

The 18-inch distance acts as a safety measure to ensure that the PEX tubing is installed in a section of the system where the temperature is more stable and less likely to cause damage. Adhering to this guideline is crucial for maintaining the durability and functionality of the plumbing system.